Roland Knapp
This notebook contains a summary of results obtained from the analysis of capture-mark-recapture (CMR) data from mountain yellow-legged frog populations in California’s Sierra Nevada. These data are collected by the Mountain Lakes Research Group, usually on an annual basis. The intent of this notebook is to provide a single file where researchers and managers can obtain information about the current status of these populations, many of which are critically important for the recovery of this species. Data from visual encounter surveys are also included in the summary to augment the results from CMR surveys. This information is updated annually as data from the most recent summer field season is analyzed.
In the following summary, populations are categorized as “Donor populations”, “Translocated populations”, and “Reintroduced populations”, and within these categories populations are identified by their five-digit site id. Unless otherwise noted, frogs in all populations are infected with the amphibian chytrid fungus, Batrachochytrium dendrobatidis (Bd). Unlike the severe effects caused by Bd following its initial arrival in these populations, usually decades ago, many of these populations are now co-existing with Bd. The reasons for this changed dynamic are under study, and appear to involve evolutionary changes in frogs that have made them less susceptible to chytridiomycosis, the disease caused by Bd.
“Donor” populations include populations from which frogs are collected for translocations and in which CMR-based estimates of survival guide decisions on how many frogs can be collected without impacting population viability. This category also includes populations that are not used as donor populations, but are particularly important because of unique characteristics such as remaining in a Bd-naive condition. Given the paucity of information about Bd-naive populations, CMR surveys could provide important insights into frog dynamics in the absence of Bd infection.
Unlike nearly all other populations at which CMR surveys are being conducted, this population is Bd-naive. The objective of the surveys at this site is to describe the population dynamics of MYL frogs in the absence of Bd infection. This population was chosen for surveys because the small size of the habitat produced a relatively small population at which CMR would likely be feabible (unlike the populations in larger lakes, that often contain thousands of adult frogs). No translocations/reintroductions have been conducted to this site, so no estimates of frog survival are produced by the mrmr package.
This site contains two ponds (11008, 11009) located within 50 m of each other. Both ponds have similar area and depth. However, throughout the summer the upper pond (11008) appears to drain via subsurface flow to the lower pond (11009). As a result, the surface elevation of 11008 typically drops by ~ 50 cm over the summer while the elevation of 11009 stays constant. That contributes to a relatively rocky and unvegetated shoreline at 11008 and one at 11009 that is dominated by sphagnum moss, often creating overhanging banks that are highly preferred habitat of MYL frogs. This habitat difference results in very different population structures at the two sites. 11008 typically contains a small adult population of ~ 20 large adult frogs, and 11009 typically contains a much larger population (~ 100-200 adults). Both ponds contain similar numbers of tadpoles (~ 500-1000).
This site includes two adjacent and relatively small, shallow ponds (72808, 72336) connected by a perennial stream. that is exposed to large avalanches during severe winters. These events typically cause very high mortality of adults and resulting high variability in frog population size (~ 50-250). We anticipated collecting adult frogs from this population in 2017 for a translocation, but avalanche impacts during the previous winter produced high frog mortality and the resulting small population size precluded any frog collections. It is hoped that the population will rebound and be able to serve as a donor population in the future.
This population was established via translocation of 60 adults in 2016. This action was conducted by the National Park Service to create another population in a basin that contains several Bd-naive populations. The translocated frogs were not PIT tagged before release, and were monitored occasionally by NPS staff using VES. CMR surveys were initiated in 2020. The objective is to provide insights into the population dynamics of translocated frog populations in the absence of Bd infection, for comparison to dynamics of Bd-positive translocated populations.
Estimated population size is ~ 35-40 adult frogs. In the absence of much recruitment yet to date, this suggests relatively high survival of the translocated frogs.